Stop mechanism for jacks



May 30, 1933.

R. sTATz 1,912,236

STOP MECHANISM FOR JACKS Filed July 7. 1932 2 Sheets-Sheet l May 30?; E933.. R. STATZ sToP MECHANISM FOR JAcKs Filed July '7, 1932 2 Sheets-Sheet 2 www? Patented May 3i), 1933 UNITED STATES .PATENT "OFFICE ROBERT STATZ, 0F RACINE, WISCONSN, ASSIGNOR TO WALKER MANUFACTURING COMPANY, OF RACINE, WISCONSIN, A 'CORPORATION OF 4VTESCONSIN STOP MECHANISM FOR JACKS Application led .July 7', 1932. Serial No. 621,1?4.

j This invention relates to a new and improved stop mechanism for lifting` jacks adapted to positively stop the operation of the driving mechanism when the lifting or load-supporting member has reached either its upper or lower limits of travel.

Although this improvedl lifting mechanism might be used in a variety of forms of jacks, it is especially adapted for incorporation in heavy-duty screw jacks designed for raising or lowering very heavy loads. Such jacks include one or more lifting :screws and a rotary driving member through which power is applied to elevate the load-lifting member. In order to obtain the necessary lifting power without requiring the application of undue effort to the manually operated driving means, a very large gear reduction is used. Although stop detents or lugs are used on the various interiitting lifting and guide members so as to prevent these members from being completely projected from one another, the power that may be applied is so great that there is danger of shearing koff these stop ydevices if excessive power is applied to the operating means after thev load-supporting member reached its upper limit of travel. The vstop mechanism forming the subject matter of this invention is adapted to positively stop the rotary movement of the main driving member from which power is applied to the screws when the load-supporting member has reached either limit of its vertical travel. The stop mechanism comprises a pair of intermeshing gears, one of which is formed on or turns with the rotary driving member, and the other of which is an idler. These gears have an unequal number of teeth, and cooperating stop elements are formed on each of the gears adjacent the intermeshing `gear teeth, these elements coming into engagement with one another after .a predetermined number of rotations of the `driving member in either direction. i

The principal object of this invention is to provide an improved stop mechanismy for lifting jacks, of the type briefly described hereinabove and disclosed more in detail in the specications which follow..

has Y Another object is to provide improved 'l means for preventing complete separation of the telescoped lifting members of a multiple screw jack, or injury to the parts, when the jack is extended or contracted to the limit of its vertical movement.

Another object is to provide .an improved stop mechanism for lifting acls comprising a pair of intermeshing gears and .stop elements carried by the respective gcarswhich engage after a predetermined number of rotations of the gears.

Other ob'ects and advantages of this invention will be .more apparent from the following detailed description of one approved .form of mechanism built and operating according to .the principles of this invention.

In the accompanying drawings.:

Y Fig. 1 is a centralvertical section through lone form of multiple-screw lifting jack with the improved stop mechanism incorporated therein.

Fig. 2 is .a partial horizontal section taken substantially on theline 2 2 of Fig. 1.

Fig. 3 is a detail vertical section, taken substantially on the line 3 3 of Fig. 1.

Fig. 4 isa central vertical section through the idler gear.. v

Fig. 5 is a detached perspective-view showing the two gear elements of the stop mechanism in assembled relation..

It will be understoedjthat .the lifting'j ack shown in Fig. 1 is of .a known type .and is disclosed merely by way of example to illustrate one type of jack for use with which this improved stop mechanism -is particularly adapted. The jack housing 1 comprises a base plate .2, a lower portion 3 adapted .to house the various mov-ing elements of the jack, and an upper tubular guide portion-4 through which the lifting elements of the jack are projected upwardly. The load to be lifted is carried by -a hea-d or rest 5 mounted at the upper end ofv any inner tubular lifting screw 6 which is externally threaded `to'engage within the nut 7 formed in the upper end portion of the outer tubular lifting member 8 which is guided for .both vertical .and rotary movements within the guide portion lofthe standard. The

outer tubular lifting screw 9 telescopes freely over the inner screw 6 and is externally threaded to engage within the nut 10 formed within the lower end portion of the outer, lifting member 8. The driving member in the form of a rather large horizontally disposed bevel gear 11 has a central annular hub portion 12 in which is iixedly mounted and supported the lower end of the outer lifting screw 9. The hub 12 of the driving member is rotatably supported by an annular roller bearing indicated generally at 13, which in turn is supported from the base plate 2. It will be understood that `all of the parts just described are coaxial about the same vertical axis. A non-circular guide posit 14 is anchored at 15 in the base plate 2 and over this post is telescoped a hollow noncircular guide member 16 which fits within a non-circular cavity formed within the inner screw 6. It will be apparent that these three members 14, 16 and 6 are permitted free longitudinal movements over one another, but due to their non-circular interftting portions relative rotation between the parts is prevented. Since the post 14 is anchored within the base plate 2, it will be apparent that the load-supporting screwr 6 is held against rotation at all times, regardless of the presence or absence of a load upon the head 5. The hollow guide member 16 is formed with an inwardly extending detent or stop portion 17 which projects into a recess 18 formed in the post 14, this recess terminating short of the upper end of t-he post. The member 16 is formed at its upper end with outwardly projecting stop members 19 which engage 1n slots or recesses 20 in the inner screw 6, these slots terminate ing short of the lower end of the screw. The extreme upper position to which the lifting head 5 may be elevated is limited by the engagement of detent 17 with the upper end of recess 18 and the enga-gement of detents 19 with the lower ends of slots 20.

The means for rotating the driving member 11 comprises a bevel pinion 21 meshing with the beveled teeth 22 formed on the driving member, said pinion 21 being formed integrally with a spur gear 23 and journaled on the stub shaft 24 which is suitably supported in standard 1. A relatively small spur pinion 25 is formed on the spindle 26 which is rotatably mounted in the standard and which is formed in its exposed head 27 with a non-circular recess 28 in which is engaged the correspondingly shaped end of the removable crank or other means by which vrotary `motion is imparted to the driving members. It will be apparent that this reduction gearing will greatly increase the power that may be applied through the rotary driving member 11, and since the screws have a relatively small pitch adequate power is obtained for lifting a very heavy load without the application of any excessive turning force to the spindle 26. The power that may be thus obtained is in fact so great that if the operator continues to apply ez;- cessive force to the driving means after the normal upper limit of elevation of the jack has been reached, there is danger of twisting the tubular guide sleeve 16 or shea-ring olf the stop device 17 or 19, unless means is provided for positively preventing further movement of the driving gears when this maximum elevation of the jack has been attained.

The present invention relates to means for positively preventing further rotation of the driving member 11 when the lifting head 5 has reachedeither its upper or lower limits of travel. An idler gear 29 having the annular series of spurteeth 30 is freely journaled on the horizontal shaft 32 mounted in one side of standard 1. The teeth 30 mesh with an annular series of upwardly projecting gear teeth 33 formed on the driving member 11 interiorly of the beveled teeth 22. The gears 30 and 33 have an unequal number of teeth. In the present example there are 19 of the teeth 30, and

v23 of the teeth 33. One of the teeth 30 on spur gear 29 is extended laterally so as to form a stop element 34. A cooperating stop element 35 is formed on the driving member 11 opposite the space 36 between two of the teeth 33. The 'stop elements 34 and 35 are so disposed that their respective paths of rotation have one point in common, that is, if the gear teeth 30 and 33 were to mesh in oneparticular position the stop elements 34 and 35 would have to be positioned in the same space at the same time, an obviously impossible condition. In the example here shown, with the stop elements 34 and 35 in engagement, the rotary driving element 11 carryingI the gear`33 can make approximately 19 rotations in one direction before the elements 34 and 35 again engage. The driving member 11 may then be rotated approximately 19 turns in the opposite direction before the elements 34 and 35 are brought back to their original position of engagement. The number of rotations permitted the driving element is slightly less than 19 since the stop elements 34 and 35 will engage one another before the element 34 has been brought exactly into a vertical position, as will be apparent from Fig. 3. In general, the number of rotations permitted the driving member 11 will correspond to the number of gear teeth on the gear 29. The number of teeth 33 inthe annular gear formed'on'the driving member llimay be varied through wide limits, providing there is no common factor for the number' of teeth on the two intermeshing ygears of the stop mechanism. For example,

the gear 33 might have any number of teeth rfi ' ing member.

from 2O to 37, and the driving member 11 could make approximately 19 revolutions in either direction. However, if there were 3S teeth in the annular series 33, the driving member 11 could only make one revolution in either direction befo-re it would be stopped. A simple rule is to find the least common multiple of the number of teeth on the two intermeshing gears, and then divide this least common multiple by the number of teeth on the master gear, that is the teeth on the driving member whose rotations are to be controlled. The quotient will be the number of revolutions permitted this driv- In the example here shown, the least common multiple of 19 and 23 is 437. Dividing this by 23 (the number of teeth in series 33) gives 19 revolutions permitted the driving member.

In designing the stop mechanism for any particular jack it must irst be ascertained how many revolutions of the driving member 11 are required to move the load-supporting member from one limit of its travel to the other. The gear 29 may then be provided with a number of teeth equal to this number of revolutions, and any convenient number of teeth may be used in the annular series 33, depending upon the proportioning and design of the parts, so long as there is no common factor between the number of teeth on the two intermeshing gears.

It will be apparent that the only additional piece of mechanism is the idler gear 29 which may be conveniently positioned in one side of the jack standard without materially increasing the size of the jack. It requires very little power to turn this idler gear, and it may be economically constructed, as well as the additional series of gear teeth formed on the driving member 11. When the driving member has made the required number of rotations, in either direction, the stop member 34 will abut against the top of the stop member 35 and prevent further rotation of the intermeshing gears in this direction. Obviously, the gears and the supporting members may be made quite strong and rigid and there is little danger of injuring these parts by the force that may be applied to the driving gearing. In the operation of a jack of this type, when the load-supporting member 5 has reached its upper limit of travel as determined by the normal stop members 17 and 19, the operator may believe that the parts have merely stuck and that further movement should be possible and will apply excessive force to the turning crank suilicient to twist the tubular guide 16 or shear off the stops 17 or 19. However, the auxiliary stop members 34C and 35 will at this time come into engagement and positively prevent further rotation of the driving gear 11 in this direction, thereby preventing injury to the tubular lifting and guide members or the normal stop devices associated therewith. In an exactly similar manner turning movement of the driving member 11 will be arrested when the loadsupporting inember5lias reached its lower limit of travel and the lifting and guide devices are completely telescoped. The 'operation of the stop mechanism is entirely `automatic and requires no attention whatever.

It will be apparentthat the master gear 33 with which the idler gear 29 of the stop mechanism meshes might be attached to or formed on any one of the rotating members of the driving mechanism instead of the main bevel gear 11, as in the example here shown, it merely being necessary that the size of the intermeshing gears and the relative number of teeth thereon be properlyfor limiting the movement of the rotary member to a predetermined number of rotations in either direction sufficient to move the lifting member from its lower to its upper limit of travel or vice versa, said lmechanism comprising a pair of intermeshing gears, one of which turns with the driving member, one gear having more teeth than the other gear, and cooperating stop elements one of which is positioned in line with the space between two teeth on one of the gears and the other of which is positioned in line with a tooth on the other gear,

the paths of rotation of the two elements having a portion in common. f

2. In a lifting Jack, in combination with` a vertically movable lifting member, a rotary driving member, and operating elements connectmgV the members, a vstop mechanism for limiting the movement of thek r rotary member to a predetermined numberl ofrotations in either direction sufficient to move the lifting member from its lower to its upper limit of travel or viceversa, said mechanism comprising an annular series of gear teeth formed on the driving member, an idler gear the teeth of which diifer in number from the first mentioned annular series and mesh therewith, one of the teeth on'the gear being of greater width than the others, and a stop abutment-located on the driving member opposite'the space between two teeth of the annular series and Ain position to engage with the wider tooth.

3. In a lifting jack, in combination with a supporting standard, a vertically *movable*V lifting member, a rotary driving member mounted in the standard for rotation about the axis of vertical movement of the lifting member, intermediatev operating elements mounted coaxially With said members for moving the lifting member vertically When the rotary member is rotated, and driving elements mounted in one side of the standard and engaging With the driving member to impart rotation thereto in eitherdirection, a stop mechanism for lim'iingthe movement of the rotary member to a predetermined number of rotations in either direction suficient to move the lifting member from its lower to-its upper limit'of travel or vice versa, said mechanism comprising an annular series of gear teeth formed on one horizontal face orp the driving member and centered about the vertical axis, an idler gear journaled on a. horizontal axis in one side ot' the standard, the teeth of said gear differing in number from the annular series and meshing therewith, and stop abutments one of Which is formed on the gear and one on the driving member adjacent the respective series of intermeshing teeth, the abutments being positioned to engage after a predetermined number oi' rotationsr of the driving member in either direction.

4. In a lifting jaclr, in combination with a supporting standerd, a vertically movable lifting member, a rotary driving member mounted in the standard for rotation about the axis of vertical movement of the lifting member, intermediate operating elements mounted coaxially with said members for moving the lifting member vertically when the rotary member is rotated, and driving elements mounted in one lside of the standard and engaging With the driving member to impart rotation thereto in either direction, a stop mechanism for limiting the` movement of the rotary member to a predetermined number of rotations in either direction sufficient to move the lifting member from its lower to its upper limit of travel or vice versa, said mechanism comprising an annular series of gear teeth formed on one horizontal :tace of the driving member and centered about the vertical axis, an idler gear journaled on a horizontal axis in one side of the standard, the teeth ot said gear differing in number from the annular series and meshing therewith, one of the teeth on the gear being extended at one side beyond the other teeth, and a stop abutment positioned on the driving member opposite the space between itWo teeth of the annular series so that the paths of revolution of the abutment and tooth extension Will have a portion in common.

ROBERT STATZ. 

